Because they each come in multiple colors, the shuffle and the nano could be way down on the list, even if, overall, they're selling like hotcakes. This kind of tracking skews the rankings a bit, doesn't it?

I don't doubt that. The main function controls I use on my iPod are skip, pause, play and volume. Nothing else much matters when I'm listening on shuffle-play (95% of the time). Those functions are more difficult with a touch than they are a click wheel. (You have to look at it first, can't do it with gloves on, etc.) In any case, I hope Apple rethinks the use of the click wheel and doesn't abandon it.